.mater {
    width: 400px;
    height: 400px;
    border: 1px solid black;
    position: relative;
    margin: auto;
}


.box1 {
    width: 200px;
    height: 100px;
    background: red;
    margin: 10px auto;
    position: absolute;
    left: 60px;
    top: 60px;
}

.box2 {
    width: 200px;
    height: 100px;
    background: blue;
    margin: 10px auto;
}

.box3 {
    width: 200px;
    height: 100px;
    background: yellowgreen;
    margin: 10px auto;
}